The filoviruses, Ebola virus (EBOV) and Marburg virus (MARV), are HHS Tier 1 Category A priority pathogens that cause severe and often fatal hemorrhagic fever (HF) in humans. There are presently no approved therapeutics for EBOV or MARV infections, and a broad spectrum post-exposure treatment conferring protection across all medically relevant EBOV species and MARV strains does not exist. Tekmira currently is developing therapeutics targeting Zaire ebolavirus (ZEBOV) and MARV formulated as Lipid Nanoparticles (LNP). Tekmira's LNP platform stabilizes encapsulated siRNA and ensures effective delivery to disease sites and target cells. The goal of this research proposal is to generate a single broad spectrum siRNA-LNP targeting the most clinically relevant MARV strains and EBOV species (ZEBOV, Sudan ebolavirus (SEBOV) and Bundibugyo ebolavirus (BEBOV)). This therapeutic will then be used in a combinatorial treatment strategy with either recombinant vesicular stomatitis virus (rVSV)-based post exposure vaccines from RPI or fully human anti-filovirus monoclonal antibodies from RP2 described elsewhere in this CETR application. This combinatorial strategy is intended to provide an effective and complementary treatment of filovirus infection that is more effective than each therapeutic alone. To overcome EBOV and MARV sequence divergence and develop a broad spectrum siRNA therapeutic, two strategies will be pursued. The first strategy (Aim 1) will identify siRNA candidates having the most activity against one or more of the EBOV and MARV species. Individual siRNAs will then be combined in a cocktail within a single LNP formulation to enable broad spectrum targeting. The second strategy (Aim 2) will allow us to reduce the number of different siRNA within the cocktail through the use of universal neutral bases which are able to pair with multiple nucleosides. Incorporation of one or more neutral bases in our siRNA sequence will allow targeting regions of incomplete sequence conservation among filovirus species. The most effective broad spectrum candidate siRNAs will then be encapsulated within a single LNP and tested for activity in nonhuman primates (Aim 3). Following these studies, a single broad spectrum siRNA-LNP therapeutic will be selected for assessment in combinatorial post exposure treatment studies in close collaboration with RPI and RP2 (Aim 4).